The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each located in a nacelle also housing a set of related actuating devices connected to its operation and performing various functions when the turbojet engine is running or stopped. These related actuating devices in particular comprise a mechanical thrust reverser actuating system.
A nacelle generally has a tubular structure comprising an air intake upstream from the turbojet engine, a middle section intended to surround a fan of the turbojet engine, a downstream section housing thrust reverser means and intended to surround the combustion chamber of the turbojet engine, and generally ends with a jet nozzle, the outlet of which is situated downstream from the turbojet engine.
In the present application, the terms “upstream” and “downstream” are defined in reference to the flow direction of the flows of air.
Modern nacelles are intended to house a dual flow turbojet engine capable of creating, by means of the fan blades, a flow of air whereof one portion, called hot or primary flow, circulates in the combustion chamber of the turbojet engine, and whereof the other portion, called cold or secondary flow, circulates outside the turbojet engine through an annular passage, also called a tunnel, formed between a fairing of the turbojet engine forming an internal fixed structure (IFS) and an inner wall of an outer fixed structure (OFS) of the nacelle. The two flows of air are discharged from the turbojet engine through the rear of the nacelle.
During landing of an airplane, the role of a thrust reverser is to improve the braking capacity of that airplane by reorienting at least part of the secondary flow of air forward. In this phase, the reverser obstructs the cold flow tunnel and orients said cold flow toward the front of the nacelle, thereby creating a counter-thrust that is added to the braking of the airplane's wheels.
The means implemented to perform this reorientation of the cold flow vary depending on the type of reverser. However, in all cases, the structure of a reverser comprises moving cowls that can be moved between a closed or “direct jet” position, in which they close that passage, and an open or “reverse jet” position, in which they open a passage in the nacelle intended for the deflected flow. These cowls may perform a deviating function or simply serve to activate other deviating means.
In the case of a cascade thrust reverser, the reorientation of the flow of air is done by cascade vanes, the cowl performing only a simple sliding function aiming to expose or cover said vanes.
The translation of the moving cowl is done along a longitudinal axis substantially parallel to the axis of the nacelle. Thrust reverser flaps, actuated by the sliding of the cowl, make it possible to obstruct the tunnel of the cold flow downstream from the cascade vanes, so as to improve the reorientation of the cold flow toward the outside of the nacelle.
The sliding of the moving cowl between its “direct jet” and “reverse jet” positions is traditionally done by multiple actuators, of the electromechanical type (for example, a worm screw actuated by an electric motor and moving a nut) or the hydraulic type (cylinders actuated by pressurized oil).
Known from the state of the art, and in particular from document FR 2,916,426, is a cascade thrust reverser whereof the cowl is in a single piece and slidingly mounted on runners positioned on either side of the suspension pylon of the assembly formed by the turbojet engine and its nacelle.
“Single-piece cowl” refers to a quasi-annular cowl, extending from one side of the pylon to the other without interruption.
Such a cowl is often referred to as an “O-duct”, in reference to the shroud shape of such a cowl, as opposed to a “D-duct” or “C-duct”, which comprises two substantially semi-cylindrical cowls each extending over a half-circumference of the nacelle.
The thrust reverser device is an integral part of this downstream part and generally follows the same O-duct or C-duct architecture.
Based on the structure of the downstream section, the maneuvering operations to access the inside of the nacelle during maintenance operations are different.
Thus, in the case of a traditional C-duct nacelle, the moving cowls are generally mounted so as to be able to be opened by pivoting around a substantially longitudinal axis of the nacelle situated near the attachment pylon of said nacelle. During maintenance operations, it therefore suffices to unlock these moving cowls along a hinge line generally separated in the lower part of the nacelle and to open said moving cowls (butterfly opening).
The same cannot be true for an O-duct nacelle. In such a configuration, the moving cowl must be maneuvered in the longitudinal axis of the nacelle, toward the rear thereof, substantially along the same path as during opening of the cowl in thrust reverser mode.
It should nevertheless be noted that for safety reasons, in particular in order to avoid any untimely opening of the thrust reverser during flight, lock systems are provided equipping the device and aiming to block unauthorized movement of the moving cowl(s).
There are generally three locks of two types per moving cowl. More specifically, there are two so-called primary locks, positioned upstream from the cowl, generally at cylinders driving the latter, so as to lock the actuators of the cowl themselves, and a so-called tertiary lock, positioned downstream from the thrust reverser device generally at a guide rail of the moving cowl in question, so as to be able to block the cowl directly itself. This tertiary lock frequently assumes the form of a locking hook capable of engaging with a shaft secured to said cowl, so as to block the withdrawal thereof along said rail.
These locks are powered by the electrical grid of the airplane and connected to the control system of the thrust reverser. Thus, on the ground, these locks are in the locked position and are generally no longer electrically maneuverable from the airplane.
One example of a tertiary lock is described in document US 2006/0101806.
It will therefore be understood that a so-called tertiary lock is thus capable of preventing opening of the moving cowl for maintenance operations in the case of an O-duct nacelle, whereas it is does not present any hindrance for a C-duct nacelle.
The disengagement of the tertiary bolt during maintenance may either be done electrically, using the same principle as its nominal control from the airplane, or manually.
In order to reduce the time needed to access the engine, electrical control is preferable. Such a choice, however, involves several constraints, i.e., in particular:                the electrical power supply and electrical maintenance command need to come from the electrical power supply grid and a control grid that are generally dedicated to maintenance, and in any case segregated from the nominal electricity and control grids of the airplane,        opening is able to be commanded by an operator at the nacelle,        the command is used only for the time needed to translate the moving cowl, so as to avoid any overheating of the electrical opening device of the lock, and in particular the motor,        the opening of the lock need be quick enough and any impact of the translated moving cowl on the lock must be avoided.        
Furthermore, in the case of a manual system, the ease of maneuvering of course depends on the accessibility of said lock. It is in particular increasingly frequent for the tertiary lock to be positioned near the pylon, close to a so-called 12 o'clock beam serving as a guide rail or runner most capable of reacting forces optimally. Under such conditions, it is then hard to access said lock manually and without a ladder.
In the case of C-duct nacelles for example, the tertiary locks are placed substantially at 6 o'clock, and more specifically at a middle actuator of the concerned cowl, and are therefore easily manually accessible, in particular to inhibit them if necessary.
In general, the existing solutions for C-duct nacelles cannot be transposed to O-duct nacelles, due both to the different accessibility and the maneuvering needs.
In fact, as previously mentioned in the case of C-duct nacelles, the tertiary locks do not need to be open to allow opening of the moving cowls. As a result, the need to operate the tertiary lock manually is rare, the potential bother furthermore being reduced due to the location of the tertiary locks at 6 o'clock.
Thus, the current solutions available for an O-duct nacelle having a tertiary lock situated near the pylon only meet inhibiting needs, upon failure of that lock.